The experiments proposed herein are designed to yield an accurate and relatively detailed picture of the immune response to SV40 TSTA during the course of primary SV40 virus-induced tumorigenesis, with particular emphasis upon the balance among those factors - cell-mediated immunity, humoral immunity and free circulating tumor-associated antigen (TSTA) - which are thought to govern the ultimate fate of the tumor in the host. Immunologic parameters which may govern resistance or susceptibility to SV40-indiced neoplasia will also be investigated. Finally, immunotherapeutic protocols will be studied for their ultimate effects on the fate of the tumor in the host. This final outcome of tumor development will be correlated with the cell-mediated immune response of the host to SV40 TSTA after immunization, as well as with the levels of free antigen and/or circulating blocking factors elicited in the host. The system in which these experiments will be conducted bears a very close resemblance to that model presently thought to represent the events leading to human neoplasia. The results obtained in this model tumor system may therefore have great potential for clinical applicability in the design of immunotherapeutic protocols for the successful treatment and/or prevention of human cancer. BIBLIOGRAPHIC REFERENCES: Blasecki, J.W., Thymus-Derived Lymphocyte-Dependent Rejection of Syngeneic SV40-Transformed Tumor Cells in Hamsters. Proc. Amer. Assoc. Cancer Res., 1977, In press. Houston, K.J. and Blasecki, J.W., Effect of SV40 Tumor Growth Upon Cellular and Humoral Immune Responses in Inbred Hamsters. Abstr., Ann. Mtg. Amer. Soc. Microbiol., 1977, In press.